1. Technical Field
The present invention relates to a method for forming fine wiring, in particular, a method for forming fine wiring which can prevent spreading of droplets on the substrate, increase the width without bulging during high resolution printing or repeated printings, and increase adhesiveness between the substrate and wiring.
2. Description of the Related Art
Ink-jet technique allows precise ejection of substances to desired positions with desired quantity. Since the ink-jet technique does not require the photolithography process, which uses a mask in patterning, by computer engaged direct printing, and have an advantage that printing on a portion having prominence and depression is possible, many efforts are endeavored to apply this technique in industrial fields.
However, in forming fine wiring, the ink-jet technique has limitation that if droplets ejected from a head nozzle to a surface that has not been specially treated diffuses more than 3 times on the surface of a substrate. Because about 10-30 picoliter of a droplet is ejected by a present industrial ink-jet head and the diameter of the droplet is 27-39 um, if the droplet diffuses more than 3 times, it is difficult to form fine wiring of below 100 um. Therefore, in order to form fine wiring, prevention of spreading of ink-jet droplets via surface treatment of the substrate is required. However, since spreading and surface adhesiveness between droplets and substrate have negative correlation, surface treatment for preventing spreading generally decreases surface adhesiveness between droplets and substrate simultaneously.
Furthermore, for application of substrate wiring, more than 10 um width of wiring is needed. However via the present ink-jet technique wiring only below 1 um wiring is formed, and thus repeated printings are required. However repeated printings cause spreading of wiring. Further, it is known that another method to increase the width of wiring, high resolution printing, can cause bulging which means aggregation of bursting of some parts of printed wiring, if the droplets are stacked more than a certain degree on the surface that has been treated to prevent spreading.
Therefore, in producing a printed circuit board of fine wiring via ink-jet technique, a new method that can prevent spreading of droplets, is available for high resolution printing and repeated printings to increase the width of wiring, and can assure the adhesiveness between wiring and substrate is required.